PMR writer with graded side shield

ABSTRACT

A perpendicular magnetic recording (PMR) head is fabricated with a pole tip shielded laterally by a graded side shield that is conformal to the shape of the pole tip at an upper portion of the shield but not conformal to the pole tip at a lower portion. The shield includes a trailing shield, that is conformal to the trailing edge of the pole tip and may include a leading edge shield that magnetically connects two bottom ends of the graded side shield.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the fabrication of a perpendicular magneticrecording (PMR) write head whose main pole is at least partiallysurrounded by shields formed of magnetic material. In particular itrelates to such a head that is shielded at its sides by shields that arenon-conformal to the shape of the main pole.

2. Description of the Related Art

The increasing need for high recording area densities (up to 500 Gb/in²)is making the perpendicular magnetic recording head (PMR head) areplacement of choice for the longitudinal magnetic recording head (LMRhead).

By means of fringing magnetic fields that extend between two emergingpole pieces, longitudinal recording heads form small magnetic domainswithin the surface plane of the magnetic medium (hard disk). As recordedarea densities increase, these domains must correspondingly decrease insize, eventually permitting destabilizing thermal effects to becomestronger than the magnetic interactions that tend to stabilize thedomain formations. This occurrence is the so-called superparamagneticlimit. Recording media that accept perpendicular magnetic recording,allow domain structures to be formed within a magnetic layer,perpendicular to the disk surface, while a soft magnetic underlayer(SUL) formed beneath the magnetic layer acts as a stabilizing influenceon these perpendicular domain structures. Thus, a magnetic recordinghead that produces a field capable of forming domains perpendicular to adisk surface, when used in conjunction with such perpendicular recordingmedia, is able to produce a stable recording with a much higher areadensity than is possible using standard longitudinal recording.

Since their first use, the PMR head has evolved through severalgenerations. Initially, the PMR head was a monopole, but that design wasreplaced by a shielded head design with a trailing edge shield (TS),which provides a high field gradient in the down-track direction tofacilitate recording at high linear densities. Side shields (SS) thenbegan to be used in conjunction with the trailing edge shields, becauseit was necessary to eliminate the fringing side fields in order toincrease writing density still further. To further reduce the fringingin the down-track direction, thus reducing the length of the writebubble down the track and improving write performance at a skew angle,an optional leading edge shield (LS) was also proposed, making the writehead four-side shielded.

Referring to FIG. 1 a, there is shown an ABS (air bearing surface)planar view of a prior art PMR writer with a main pole (10) shielded ina (partial) wrap-around manner by a shield (20) that has twosymmetrically disposed side portions (30) (hereinafter called a sideshield (SS)) and a trailing edge portion (40) (hereinafter called atrailing shield (TS)). Note that a horizontal dashed line (75) indicatesan imaginary boundary between the upper portion of the shield that maybe considered the trailing edge portion (40) and the two laterallydisposed portions (30), continuous with the trailing edge portion (40),taken together, will be considered the side shield (SS). The trailingshield (TS) (40) provides a down-track field gradient for improvedwriting at higher areal density and the side shield (SS) restricts thefringing of the magnetic field, thereby improving the adjacent trackerasure (ATE) performance. Typically a write gap material (59) fills thespace between TS and main pole.

As can be seen in this ABS view, the inner edges (31) of SS are shapedto be conformal with the sides (11) of the main pole, producing agenerally uniform gap (50) between the inner edges of the shields andthe lateral sides (11) (outer surfaces) of the main pole. Forsimplicity, we shall call such a shield configuration “conformal to themain pole”, symbolized iSS.

Conformality is here (and hereinafter) meant to indicate the fact thatwhen viewed in the ABS plane, edges or edge portions (31) of the innersurface of the shield (its inner periphery) have the same shape as theouter edges of the main pole and are typically parallel to, butdisplaced from the pole itself so as to produce a uniform spacingbetween the pole and the shield. A non-conformal portion of the shieldwould encompass a portion of its inner edge (inner periphery) that isnot of a similar shape to that of the pole, that is displaced from thepole in a horizontal (or vertical) direction and, therefore, ischaracterized by a non-uniform spacing between the shield innerperiphery and the outer edges of the pole.

Referring next to FIG. 1 b, there is shown an ABS (air bearing surface)view of a prior art PMR writer with a main pole (10) partially shieldedin a wrap-around manner by a shield (25) that has a symmetricallydisposed side shield (SS) portion (35) and a trailing edge portion (40)(hereinafter called a trailing shield (TS)). Note that a horizontaldashed line (75) indicates the imaginary boundary between the portion ofthe shield that may be considered the TS (40) and the laterally disposedportions (35) that, taken together, may be considered the SS. Unlike theshield configuration of FIG. 1 a, this configuration has a side shieldthat is not conformal to the main pole, producing generally non-uniformside gaps (55 a, 55 b). We shall describe such a shield as being“non-conformal to the main pole,” symbolized NCiSS. The NCiSS structureproduces a higher strength field than the iSS structure, whereas the iSSstructure has less side fringing due to the closeness of the sideshields.

An additional issue with the NCiSS is that the shape of the SS isdefined by a separate photo-mask process after the main pole shapingprocess has occurred. Due to the difficulty in aligning two separatemasks, the left and right side gaps (55 a) and (55 b), will generallynot be symmetric. The iSS configuration does not have this problembecause the SS are self-aligned with the main pole allowing an atomiclayer deposition (ALD) process to create a symmetric gap.

It is therefore the object of this invention to address the issuescaused by shield asymmetries and non-uniformities and their effect onon-track and off-track performance.

Issues relevant to shield materials are described in the prior arts. Forexample, Terris et al. (U.S. Pat. No. 7,068,453) discloses side andtrailing shields formed of a soft magnetic material.

Gao et al. (U.S. Pat. No. 7,441,325) discloses a trailing shield formedof NiFe.

Nix et al. (U.S. Pat. No. 7,367,112) teaches the formation of a mainpole with trailing and side shields.

Guan et al. (U.S. Pat. No. 7,322,095, assigned to the present assignee)teaches a wrap-around shield, as do Jiang et al. (US Patent Application2009/0154026) and Hsiao et al. (US Patent Application 2009/0154019).

Sasaki et al. (U.S. Pat. No. 7,558,020) discloses a trench etched inalumina and filled with a magnetic layer to form the main pole.

Han et al. (US Patent Application 2009/0091862) teaches conformal sideshields around the main pole. This Application is assigned to the sameassignee as the present invention.

Zhou et al. (US Patent Application 2009/0052092) teaches that theinsulating layer through which the main pole is etched can be alumina orsilicon dioxide. This Application is assigned to the same assignee asthe present invention.

None of the prior art cited above address the problem addressed by thepresent invention nor do they disclose the structures and materials ofthe present invention.

SUMMARY OF THE INVENTION

A first object of this invention is to design and fabricate a shieldconfiguration that improves both the on-track and off-track performanceof a PMR write head.

A second object of the present invention is design and fabricate a PMRwrite head shield that avoids the side gap asymmetries that characterizenon-conformal-to-main pole shields (NCiSS).

A third object of the present invention is to satisfy the first twoobject with either a shield that partially surrounds the main pole orcompletely surrounds (wraps around) the main pole.

These objects will be achieved by means of a partially or completelywrap-around shielded write head whose main pole (MP) is surrounded onits sides and trailing edge, or its sides and both its leading andtrailing edges, by a graded shield that is conformal to the MP at itstop (trailing edge) portion yet is non-conformal to the MP at its bottom(leading edge) portion.

The graded shield can be advantageously made by replacing the typicalalumina substrate (Al₂O₃) having a cavity within which the main pole isformed, by a bi-layer substrate, formed of MO/Al₂O₃, where MO symbolizesan oxide different from Al₂O₃, for example SiO₂, (where M═Si) which canbe etched by RIE (reactive ion etch) together with the Al₂O₃ but isselective against a chemical etch of the Al₂O₃ using an etchant such asEDTA (Ethylene Diamine Tetra-acetic Acid).

Referring to FIGS. 2 a and 2 b, there are shown schematic ABS views of apartially surrounding PMR shield that will satisfy the objects of thepresent invention (FIG. 2 a) and a completely surrounding PMR shieldthat will also satisfy the objects of the present invention (FIG. 2 b).

FIG. 2 a shows the ABS shape of a main write pole (MP) (10) that ispartially surrounded (top and sides) by a shield (60). The ABScross-sectional shape of the pole here is substantially trapezoidal andis symmetric about a perpendicular bisector (15) of its top (17) andbottom (19) edges, but is not symmetric about a horizontal axis (77)that is perpendicular to the vertical bisector.

The top portion of the shield (40), which is above the horizontal dashedline (75), includes within the inner edge of its opening (21) the topedge, or trailing edge, (17) of the pole. We may call this portion thetrailing edge portion of the shield, denoted TS. The side portion of theshield, denoted SS, which is below TS, is formed of two portions, (70)and (80). Portion (70) is between the two horizontal dashed lines (75)and (77). It has inner edges (31) that are conformal to the pole in theregion between (75) and (77), producing a uniform side gap (55) oneither side of the pole in that region. The bottom portion of the sideshield (80), the portion that is below horizontal line (77), includeswithin the inner periphery of its opening a portion below the horizontalaxis (77) that is not conformal to the pole, producing a non-uniformside gap (57). We shall denote this SS a graded side shield.

The vertical height of the portion of the main pole that is conformallysurrounded by the shield is denoted h, which can be between 20% and 80%of the entire height of the pole tip. The side edge of the bottomportion of the side shield makes an angle α (24) with the vertical (15),which can be anything between 0° and 30°.

The ABS shape of the pole tip in this example is a symmetric trapezoidwhose two parallel sides are the (narrower) leading edge (19) and(wider) trailing (17) edge and whose two, equal length non-parallelsides are the tapered sides of the pole. The trapezoid, as alreadynoted, is symmetric about the line (15) bisecting the two parallelsides. The separation between the inner edge of the upper portion of theshield (21) and the trailing edge of the pole (17) is called the writegap (59) and it is typically between approximately 15 and 40 nanometers(nm) in width.

The bottom portion (80) of the side shield, is not conformal to the mainpole. The portion of the MP that is surrounded conformally (70) has aheight h, which can be between approximately 20% and 80% of the totalheight of the MP, denoted MPh. The non-conformal lower portion of the SS(80) makes an angle, α, (24) with the vertical (15), which angle can bebetween approximately 0° and 30°. The space between the side shield (SS)and the side edges of the pole tip is called the side gap and it istypically between approximately 30 and 200 nm in width.

Referring now to schematic FIG. 2 b, there is shown a graded shield (65)that completely surrounds a main pole (10) that is substantially thesame as the main pole of FIG. 2 a. This shield can be thought of as thepartially surrounding graded shield of FIG. 2 a, to which a leading edgeshield (100) has been added (below horizontal dashed line segments (85))so as to physically and magnetically connect the lower ends of the twoSS (35) at the positions of the dashed line segments.

Like the shield of FIG. 2 a, the completely surrounding graded shield(65) is conformal to the main pole along the inner edge of a top portion(70), but is non-conformal along the inner edge of a lower portion (80).Again, like the shield of FIG. 2 a, the height of the main pole portionthat is conformally shielded is h, which can vary between approximately20% and 80% of the entire main pole height, denoted MPh, (MPh=distancebetween its upper (17) and lower (19) edges). Similarly the angle, a, bywhich the lower portion of the shield deviates from the vertical (i.e.,angle between the inner edges of the shield and the vertical bisector ofthe pole tip) and, creates the non-conformality, is betweenapproximately 0° and 30°.

Referring to FIG. 3 and FIG. 4, there are shown graphical results ofsimulations to compare the results of using a writer shielded with priorart conformal side shields (iSS) (horizontal dashed line), with theresults using the graded side shields of the present invention.

FIG. 3 plots on the vertical scale the maximum vertical field(H_(y max)) in Oe and on the horizontal scale the height h in nm asdefined above. The side gap width is 80 nm.

FIG. 4 is a plot of the overwrite (OW) at a fixed 80 nm erase width vs.h. Side gap width is 80 nm as in FIG. 3. Both the overwrite and thefield increase as h decreases.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a is a schematic ABS view of a main pole tip of a PMR write headthat is partially surrounded by a prior art type shield that isconformal to the shape of the main pole tip.

FIG. 1 b is a schematic ABS view of a main pole tip of a PMR write headthat is partially surrounded by a prior art type shield that is notconformal to the shape of the main pole tip.

FIG. 2 a is a schematic illustration of an embodiment of the presentgraded shield invention, showing a partially shielded PMR write headwith shields that are conformal along an upper portion of the main poleand non-conformal along a lower portion.

FIG. 2 b is a schematic illustration of an embodiment of the presentgraded shield invention, showing a completely shielded PMR write headwith shields that are conformal along an upper portion of the main poleand non-conformal along a lower portion.

FIG. 3 is a schematic graphical representation of the comparison ofmaximum vertical field vs. h (the height of the main pole that isconformally shielded) for the performance of a prior art conformallyshielded writer (shown as a horizontal dashed line) and an embodiment ofthe graded shield of the present invention.

FIG. 4 is a schematic graphical representation of the comparison ofoverwrite (OW) performance as a function of h (the height of the mainpole that is conformally shielded) of a prior art conformally shieldedwriter (shown as a horizontal dashed line) and an embodiment of thegraded shield of the present invention.

FIGS. 5 a-g are a series of schematic illustrations showing anembodiment of a process flow by which the graded shield write head ofthe present invention may be fabricated.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiment of the present invention is a graded shield andits method of formation. The graded shield may partially or completelysurround the main pole of a PMR write head. The shield is termed“graded” to denote a sense that its shape changes from a portion that isconformal to the main pole to a portion that is non-conformal, therebyproviding in a unique way at least the advantages normally associatedwith both prior art conformal shields and prior art non-conformalshields. The parameters describing the degree of gradation are h, theheight of that portion of the pole tip that is conformally surroundedand a, the angle with respect to vertical made by the side shield alongthat portion that is non-conformal with the main pole. Thecharacteristics of the graded shield will now be further elucidated byreference to a process flow sequence by which it may be fabricated.

Referring first to FIG. 5 a there is shown the deposition of a bi-layerdielectric substrate, which will serve to create a cavity within whichto plate a main pole and surrounding graded side shields. The bi-layeris itself formed on a substrate, which in this embodiment is a RIE(reactive ion etch) etch-stop layer (200), such as a layer of Ru formedto a thickness of between approximately 20 and 200 nm. As we shall notelater, the substrate can also be a lower shield on which the sideshields, SS, and trailing shield TS are formed.

On this substrate layer (200) is then formed the bi-layer, which is afirst layer formed of an oxide, denoted MO, where M is the element to beoxidized (other than Al). In this case, MO is an oxide of Si (i.e.,M═Si) namely SiO₂ (300) formed to a thickness between approximately 20and 150 nm. On the layer of SiO₂ is then formed a layer of Al₂O₃, (400),to a thickness between approximately 150 and 400 nm to complete thebi-layer. It is noted that the lower layer (300) is deposited to athickness that is at least the main pole height, MPh, minus h (MPh−h),whereas the upper layer (400) is deposited to a thickness that is atleast the write gap thickness, WG, plus h, (WG+h), where h is thepreviously defined height of the pole that is conformally surrounded bythe side shields.

Referring next to FIG. 5 b, there is shown a schematic illustration ofthe fabrication of FIG. 5 a now having a cavity (700) etched within it,using a RIE process. The cavity is etched through layers (400) and (300)and terminates at layer (200). In this embodiment, the cavity is formedwith a symmetric trapezoidal vertical cross-sectional shape, which issubstantially the desired cross sectional shape of the main pole tip atits ABS emergent surface. However, other cross-sectional shapes could beenvisioned. The width of the cavity at its widest point is approximatelybetween 0.2 and 0.4 microns (μm) and its width at the substrate (200) isbetween approximately 0 and 0.2 μm.

Referring next to FIG. 5 c, there is shown the cavity of FIG. 5 b nowlined with a non-magnetic, metallic layer, which in this embodiment is alayer of Ru (500) of thickness between approximately 40 nm and 120 nm.The lined cavity is then filled with a layer of CoFe (550) or othermagnetic alloy such as FeNi or CoNiFe to form the main pole tip. Theupper surface of the filled cavity is then planarized using a methodsuch as CMP, to reduce the overall thickness (MPh) of the pole tip tobetween approximately 50 and 200 nm and to leave a smooth and planarupper surface as shown schematically in the figure. At this point in thefabrication, the upper surface of the magnetic pole (10) may be tapered(thinned in a direction towards the ABS) at its trailing edge (upperedge in this figure) by means of ion beam milling.

Referring next to FIG. 5 d, there is shown the fabrication of FIG. 5 cwith portions of the substrate laterally disposed about the cavityhaving been completely removed by an etching process such as a reactiveion etch (RIE), which is essentially the same as the etching processused to create the cavity. The etching process can be implemented bymeans of a photomask placed over the cavity. The etch can be controlledby tuning the RIE condition to produce a range of angles α, between 0°(shown here) and 30°, the tuning being accomplished by adjusting suchparameters as plasma power, gas flow rate, etc.

Subsequent to the etch, the cavity remains surrounded by remnants ofsubstrate, including an Al₂O₃ portion (410) and a SiO₂ portion (310)whose lateral widths will finally determine the shape of the shields tobe formed.

Referring now to schematic FIG. 5 e, there is shown the results of a wetetch used to remove remnant portion (410), but to leave remnant portion(310). The wet etch can be accomplished using an etching solution suchas EDTA (Ethylene Diamine Tetra-acetic Acid).

Referring now to FIG. 5 f, there is shown schematically the depositionof a write gap layer (600), which is a layer of non-magnetic materialsuch as Al₂O₃, SiO₂ or Ru, deposited to a thickness of betweenapproximately 15 nm and 100 nm. Preferably, the method of deposition isALD (Atomic Layer Deposition) or CVD (Chemical Vapor Deposition).

Referring finally to schematic FIG. 5 g, there is shown the fabricationof FIG. 5 f with the addition of a plated layer (800) conformallycovering the write gap layer and serving as a combined sideshield/trailing shield structure. It is to be noted that if it isdesired to form a lower (leading edge) shield (as shown in FIG. 2 b) soas to completely enclose the magnetic pole, the substrate layer (200)would be an already formed leading edge shield on which the bi-layer,(300)/(400) of FIG. 5 a, is then directly formed. Since a good magneticcontact is preferred between the leading edge shield and the sideshield, the write gap layer (600) would be patterned so that a directcontact between the leading edge shield and the side shields isobtained. The patterning can be provided by depositing the write gaplayer using a lift-off mask or by depositing the layer conformally overthe entire leading edge shield and then removing laterally disposedportions (610) by an IBE process while protecting the already formedmain pole with a photoresist mask.

As is understood by a person skilled in the art, the preferredembodiment of the present invention is illustrative of the presentinvention rather than limiting of the present invention. Revisions andmodifications may be made to methods, materials, structures anddimensions employed in forming and providing a PMR head having a mainpole-tip surrounded by graded magnetic shield configuration, while stillforming and providing such a PMR head and pole and its method offormation in accord with the spirit and scope of the present inventionas defined by the appended claims.

What is claimed is:
 1. A PMR head comprising: A main pole having asubstantially trapezoidal ABS shape that is mirror symmetric about avertical bisector and characterized by four peripheral edges, includinga leading edge, a trailing edge that is parallel to said leading edgeand vertically separated from said leading edge by a main pole height,MPh, and two side edges tapering towards each other, wherein saidtrailing edge is wider than said leading edge; and a graded magneticside shield, symmetrically formed about said vertical bisector anddisposed horizontally about said main pole, wherein said graded magneticside shield has an opening defined by inner edges that are separatedfrom said two side edges of said main pole and wherein a top portion ofsaid graded magnetic side shield has inner edges that are conformal tosaid side edges of an upper portion of said main pole and produce a sidegap of uniform width thereat and wherein a bottom portion of said gradedmagnetic side shield has inner edges that are not conformal to said sideedges of a lower portion of said main pole and produce a side gap ofnon-uniform width thereat and wherein said inner edges of said bottomportion of said graded magnetic side shield slant outward to form anangle α with respect to said vertical bisector and extend downward to atleast said main pole leading edge; and a trailing shield formedvertically above said main pole, a leading edge of said trailing shieldhorizontally linking said inner edges of said top portion of said gradedside shield and being continuous with said graded magnetic side shield,wherein said leading edge of said trailing shield is uniformly separatedfrom said trailing edge of said main pole.
 2. The PMR head of claim 1wherein said side gap of uniform width and said side gap of non-uniformwidth are both filled with a side gap material.
 3. The PMR head of claim2 wherein said uniform separation between said trailing shield and saidtrailing edge of said main pole forms a write gap that is filled withwrite gap material.
 4. The PMR head of claim 3 wherein said side gapmaterial and said write gap material are selected from the group ofnon-magnetic materials Al₂O₃, SiO₂ and Ru.
 5. The PMR head of claim 4wherein said write gap material and said side gap material is depositedin a layer to a thickness between approximately 15 nm and 100 nm.
 6. ThePMR head of claim 1 wherein said upper portion of said main pole has aheight, h, that is between approximately 20% to 80% of said main poleheight, MPh.
 7. The PMR head of claim 1 wherein said angle α is greaterthan 0° and less than or equal to 30° .
 8. The PMR head of claim 1further including a leading edge shield that magnetically connectsbottom edges of said side shield.